This invention relates to a power circuit for the horizontal deflection yoke of a cathode ray tube utilizing a raster scan for the display.
One purpose of the invention is to provide a stable, low cost, power efficient circuit capable of operating a horizontal deflection yoke of a cathode ray tube as used in a raster scan application, such as in television and computer monitors. The constant current power circuit may be used in other applications, such as in a television camera or other electronic pick-up device which requires horizontal deflection.
The conventional circuit normally requires a flyback transformer for optimum operation. Further, the conventional circuit also requires another transformer for base switching of the flyback transistor. The flyback deflection and base transformers contribute substantially to the cost, size and weight of the conventional circuitry. Also, losses in these components adversely affect the efficiency of this circuitry. Further, the input power to the conventional circuit is obtained from the power source in a transient manner as opposed to the constant current power circuit of the present invention. The advantages of the present invention in this regard are: one, the elimination of transient loads on the dc power source thus allowing optimum design of the power source; and, two, the prevention of voltage variations and transients on the dc power source from creating undesirable spurious modulation of the horizontal deflection.
It is an object of the present invention to provide a new and improved power circuit for the horizontal deflection yoke of a cathode ray tube which eliminates the two transformers, and for some applications the linearity coil.
The conventional horizontal deflection yoke control circuit includes a switching transistor shunted by a flyback capacitor for providing frequency control of the horizontal oscillations in the yoke flyback circuit, and resetting at the proper time to create the sawtooth current waveform in the yoke. It is the sawtooth current waveform which provides the desired horizontal raster scan which is utilized in cathode ray tube devices, such as television receivers.
The amplitude of the horizontal oscillations in the conventional circuit is directly proportional to the level of the dc voltage supplied from a regulator transistor, and this amplitude is directly related to the width of the raster display. Hence, the width of the display is a function of the dc input voltage.
The standard procedure for providing the input power is through a constant voltage dc source, typically utilizing a transformer and a linearity coil. Correction for the pin cushion effect in the conventional circuit requires voltage modulation of the constant voltage dc power source.
It is an object of the present invention to provide a new and improved supply circuit incorporating a constant current dc power input rather than a constant dc voltage input, and eliminating the transformers and coils. A further object is to provide for temperature compensation of the constant current power input in order to reduce environmental effects, and to allow pin cushion correction by current modulation of the constant current power input.
It is another object of the invention to provide a dc coupled control circuit for the base of the the flyback switching transistor, thereby eliminating coupling transformers and permitting the switching transistor base return circuit to float on a variety of potentials, which reference potentials are negative with respect to the voltage source providing the constant current power. The reference potentials include ground.
It is a particular object of the invention to provide a new and improved supply circuit utilizing a constant current dc power source directly connected to the horizontal deflection yoke and a flyback circuit directly connected to the horizontal deflection yoke.
Other objects, advantages, features and results will more fully appear in the course of the following description.